1. Field of the Invention
The invention relates to blocks for installing aerial cable on a support cable which is attached to and extends between a plurality of poles. More particularly, the invention relates to an aerial cable installation block for installing aluminum coaxial cable for TV transmission which prevents kinking or bending of the cable during installation by providing spaced points of support for the cable.
2. Description of the Prior Art
In recent years cable television has become increasingly popular wherein TV signals are gathered by a single main antenna and distributed throughout an area by cables which are mounted on telephone and electric company poles. Individual cable drops then extend from the main supply cables to individual houses to provide a greater variety of programming and better television reception.
A usual television signal cable is a coaxial cable consisting of a thin, outer aluminum sheath with a central signal carrying conductor also formed of aluminum preferably with a copper coating. These inner and outer cables which extend coaxially are separated by a dielectric material such as extruded polyethylene or other plastic material. The spacing of the signal-carrying central conductor with respect to the outer aluminum sheath is critical since any variation in separation will affect the signal attenuation and the characteristic impedance of the cable.
Heretofore, this coaxial cable was installed by a plurality of aerial blocks, each block usually consisting of a single pulley rotatably mounted on a bracket which is supported on a support cable or messenger strand which extends between the poles. The cable is payed out from a large reel containing the cable in lengths ranging from 1,000 to 3,000 feet. Unless extreme care is taken during the installation of the cable, a small bend or kink will develop in the cable as it is being pulled through the pulleys due to the aluminum outer sheath not being strong enough to support the cable weight between the blocks. This introduces small bends referred to in the industry as "wee-wa" which when the cable is ultimately lashed to the support cable, the cable will not lie tightly against the supporting cable throughout its entire length. This results in a rough installation which increases the cost of the job since the contractor must go completely along the line and straighten the coaxial cable to get a satisfactory installation. In the event that the bends or wee-was are not removed, they will shorten the cable life approximately one third since the wind and weather conditions will loosen the lashing wires and allow rubbing between the aluminum outer sheath and support cable wearing through the sheath resulting in bad signal transmission and ultimately requiring replacement of the cable. One of the ways which reduces such unwanted bending is to place the support blocks at extremely close spacing. However, this increases the installation cost of the cable.
Various types of cable blocks have been devised with various attachments for rigidly or releasably mounting the block to the supporting cable. However, all of these known blocks use only a single point of cable support usually a rotatable pulley for the cable supporting means. Some examples of these prior art aerial blocks are shown in U.S. Pat. Nos. 856,335, 2,980,401, Re. 25,549, 3,134,575, 3,853,304, and 4,160,540.
Therefore, the need has existed for an aerial cable installation block which provides adequate support for the coaxial cable during installation to prevent bending or kinking in the cable thereby considerably reducing additional installation expense and maintenance after the cable has been lashed to the supporting strand. There is no known installation block which achieves this advantage by providing a pair of spaced supports on a relatively simple, lightweight frame member.